Waste incineration is a thermal treatment process that manages and significantly reduces the volume and mass of non-recyclable waste materials. Modern facilities, often termed Waste-to-Energy (WTE) plants, convert this combustion process into a source of usable power. This method drastically reduces the original waste volume by up to 95% and the mass by 80–85%, leaving behind a sterile ash residue. Incineration is a key component of municipal waste management, particularly where landfill space is limited.
The Core Incineration Process
The process begins with waste delivery, where collection trucks deposit their loads into a large storage area called a waste pit. Overhead cranes mix the waste to ensure uniform energy content and feed it into the furnace hopper. The waste moves through the combustion chamber on a moving grate, which continuously turns and transports the material to expose fresh surfaces to the flame. Inside the furnace, the waste is subjected to extremely high temperatures, often exceeding 850°C to 1000°C, ensuring the complete destruction of organic compounds.
Combustion air is precisely controlled and introduced in two main streams for optimal burning efficiency. Primary air (under-fire air) is supplied beneath the grate to support the main flame and cool the grate itself. Secondary air (over-fire air) is injected above the grate to create turbulence and provide oxygen for the gases released from the burning waste. Maintaining an accurate balance of temperature and oxygen minimizes the formation of incomplete combustion byproducts, such as carbon monoxide.
Recovering Energy and Managing Solid Residues
The conversion of heat produced during combustion into usable energy is the primary function of modern Waste-to-Energy (WTE) facilities. The intense heat generated is captured by water-filled tubes lining the walls, functioning as a boiler. This heated water converts into high-pressure, superheated steam, which drives a turbine generator to produce electricity for the public power grid. Alternatively, the steam can be used directly for district heating. This dual use of energy, known as combined heat and power, significantly increases the overall efficiency of the facility.
Incineration leaves behind two distinct types of solid residue. Bottom Ash is the coarse, non-combustible material—such as glass, metal, and ceramics—that falls to the bottom of the furnace. After the recovery of metals, this material can be processed and reused as aggregate in road construction. Fly Ash, in contrast, is fine particulate matter carried out with the hot flue gases, including residues captured by the air cleaning systems. Because fly ash contains concentrated heavy metals, it is classified as a regulated waste requiring specialized treatment before disposal in designated hazardous waste landfills.
Controlling Air Emissions
A comprehensive system of Air Pollution Control Devices (APCDs) is installed downstream of the boiler to treat the flue gases before release. Acid gases, such as sulfur dioxide and hydrogen chloride, are neutralized using scrubbers, which inject alkaline reagents like lime into the gas stream. Particulate matter, including fine Fly Ash, is removed using high-efficiency filters, such as baghouses or electrostatic precipitators, which capture over 99% of the particulates. To capture volatile pollutants like heavy metals and dioxins, powdered activated carbon is injected; the carbon binds these substances and is collected with other particulates. Facilities utilize Continuous Emissions Monitoring Systems (CEMs) to constantly track key pollutants, ensuring strict compliance with emission limits.